1. Field of the Invention
The present invention relates to an ion-conductive polymer electrolyte and an aluminum electrolytic capacitor configured with the same electrolyte as an electrolyte for driving the electrolytic capacitor.
2. Description of the Prior Art
Conventionally, as an electrolyte for driving an aluminum electrolytic capacitor, a solution prepared by dissolving an ammonium salt in an organic solvent having a high dielectric constant such as ethylene glycol has been used. However, there has been a possibility of leakage and evaporation of the electrolyte in the capacitor when such liquid electrolyte is used, and hence it has been impossible to obtain a reliability in operation for a long period of time.
In order to solve these problems, there has been proposed an electrolytic capacitor that is free from the leakage and evaporation of the electrolyte. Such a capacitor is configured by solidifying its capacitor element as a result of employing an ion-conductive polymer electrolyte composed of a mixture of siloxane-alkylene oxide copolymer and polyethylene oxide, as its prepolymer, and an alkali metal salt, instead of the liquid electrolyte.
However, the electrolytic capacitor using, as its electrolyte, the ion-conductive polymer electrolyte with alkali metal ions as its mobile ions has such a disadvantage that the alkali metal ions are liable to diffuse into a dielectric substance layer formed on a positive electrode of the electrolytic capacitor, and the thus diffused alkali metal ions might sometimes cause a lowering of the dielectric constant of the dielectric substance layer, and finally invite a short-circuit in the capacitor.
In order to overcome such disadvantages and deficiencies, it has been considered to use ammonium ions in place of the alkali metal ions which had been used as the mobile ions of the electrolyte constituting the electrolytic capacitor. However, it has hitherto been known that the ion-conductive polymer electrolyte which contains the ammonium ions has a very low ionic conductivity in general.
The ionic conductivity of the electrolyte constituting the electrolytic capacitor acts as an impedance of the capacitor, and when the ion conductivity of the electrolyte is too small, the impedance of the capacitor becomes large and it is difficult to use in practical point of view.
In order to enable an employment of such ion-conductive polymer electrolyte as the electrolyte for driving an electrolytic capacitor, it is an essential factor to clarify a suitable combination of various polymer mother ingredients (prepolymers) with ammonium salts for realizing an electrolyte of high ionic conductivity, but no concrete example has been clarified.
In addition, the application of the aluminum electrolytic capacitor has recently been expanded widely, and its long-term reliability during high-temperature storing has been attracting attention. For instance, a guarantee for its quality in the continuous exposure to a high temperature at 105.degree. C. for 10,000 hours, for instance, is now required to be accepted by the current market. When the polymer electrolytes were exposed to such a high temperature atmosphere, a physical and/or chemical deterioration such as cracks, contraction or dissolution (liquefaction) may be produced, and thus the exposure may cause a serious deterioration in the characteristics of the capacitor element. A solid phase electrolyte which does not suffer from any deterioration in its performance for such severe test environments has not been proposed yet.